Wireless networks have in recent years experienced a considerable increase in the amount of data being transmitted to and from wirelessly connected devices or user equipment, which term includes mobile or cell phones (including so-called “smart phones”), personal digital assistants, pagers, tablet and laptop computers, content-consumption or generation devices (for music and/or video for example), data cards, or USB dongles, etc., as well as fixed or more static devices, such as personal computers, game consoles and other generally static entertainment devices, various other domestic and non-domestic machines and devices, etc. This increase in traffic has been mainly due to the rapid and widespread uptake of smart phones, the availability of mobile broadband dongles for computers and affordable rates for consumers.
The traffic characteristics of this data traffic are very different from that of traditional mobile phones, and can be characterized by its use of a lot of background signalling and bursty traffic consisting of relatively small data packets. The introduction of machine type communications to the networks can be expected to follow this trend. As a result, wireless networks need to implement new mechanisms to cope with this new traffic and make efficient use of the available resources while providing high capacity and throughputs and minimum delays, and particularly to avoid congestion, which can result in the user equipment being in a “call blocked” state.
The user equipment is typically in one of a number of predefined activity states. These may be for example an idle state, a paging state in which the user equipment checks the paging channel for incoming paging messages at predefined time intervals, and one or more data connection states in which the user equipment can actively transmit and receive data. In general, these states use increasingly more power at the user equipment and also more network signalling.
This can be exemplified by work currently being carried out on FE-FACH (Further Enhancement to CELL_FACH (Forward Access Channel)) for Release 11 of the 3rd Generation Partnership Project or 3GPP. The system currently in use provides for a number of defined activity states for the user equipment, including an Idle state, a CELL_PCH/URA_PCH (paging channel) state, a CELL_FACH (forward access channel) state, and a CELL_DCH (dedicated channel) state. In the Idle state, the user equipment does not have an RRC (Radio Resource Control) connection and is the state having the lowest power consumption. In the CELL_PCU/URA_PCH state, the user equipment is again in a low power consumption state as it only periodically looks for incoming paging messages, and in this state does have a RRC connection. However, the user equipment needs to be in the CELL_FACH or CELL_DCH state in order to be able to perform both transmission and reception of data (including in particular “user” data, as opposed to data relating to control or management of the device and its network connection, etc. for example). In the CELL_DCH state, a dedicated physical channel is allocated to the user equipment. In the CELL_FACH state, the user equipment shares the physical channel with other user equipment, though nevertheless may have a dedicated logical channel. As is well understood, a logical channel in this context is an information stream dedicated to the transfer of a specific type of information over the radio interface and corresponds to an individual signal which can be separated or isolated from an aggregate of signals which occupy the same physical bandwidth or channel. CELL_FACH can be regarded as a transition state between the idle/CELL_PCH/URA_PCH and CELL_DCH states. Keeping the user equipment in CELL_FACH state improves power consumption for the user equipment compared to the CELL_DCH state (because the transmitter and/or receiver may be switched off for longer periods of time while no uplink data is available and during discontinuous reception or “DRX”) and also reduces the network signalling load (by avoiding radio resource control or “RRC” signalling to perform a state transition from the PCH or Idle states to the CELL_FACH state when both data transmission and reception are required). Nevertheless, the CELL_FACH state still has a higher power consumption for the user equipment than the PCH or Idle states.
The CELL_FACH state was enhanced with the introduction of downlink HS-DSCH (high speed downlink shared channel) transmission in Release 7 of 3GPP and uplink E-DCH (enhanced dedicated channel) transmission in Release 8 of 3GPP. These enhancements of the transmission channels within the CELT_FACH state provide substantial improvements compared to R99 FACH/RACH (forward access channel/random access channel), which were previously used for downlink and uplink transmissions in accordance with the original release of the WCDMA (Wideband Code Division Multiple Access) standard. Nevertheless, as the packet data traffic related to mobile and fixed wireless broadband, smart phones and machine type communications continues to increase, it becomes increasingly attractive to try to keep the user equipment in the CELL_FACH state since other states are associated with either a higher latency or a higher resource demand, and to have the user equipment operating in the CELL_FACH state in as efficient a manner as possible. In order to facilitate this type of operation, a number of further enhancements of the CELL_FACH state are being considered.
As a particular example, there are a number of reasons why it is desirable to have wireless devices or user equipment (or “UEs”) that are in the CELL_FACH state use PRACH (physical random access channel) for uplink transmissions when possible, in preference to using the enhanced uplink channel E-DCH (known as “enhanced uplink in CELL_FACH state and idle mode” in 3GPP). For example, having a number of UEs operate using PRACH reduces the chances that those UEs using common E-DCH will enter a call blocked state (for example because of a failure of the contention procedure due to a lack of network resources or because of message collision for those UEs). As another example, when the UE has small data packets to send, then it is more efficient to use the PRACH channel as the network resources can be reclaimed more quickly than those associated with the enhanced uplink channel E-DCH channel, leading to more effective use of NW resources. Also, in the case of the UE sending small data packets, the speed at which these messages can be transmitted is comparable when using PRACH and common E-DCH (as these control messages are in general small enough to be conveyed in the message part of a single RACH transmission), whereas when larger amounts of data needs to be sent, the common E-DCH channel is more efficient; sending smaller messages on the PRACH channel frees up capacity on the highly loaded common E-DCH channels for larger messages. In the present context, “small” messages may be those of a size of 360 bits or less, or less than 166 bits in specific cases. Such messages include in particular CCCH (Common Control Channel) transmission messages.
For completeness, it is finally noted that prior to the introduction of the common E-DCH in Release 8 of 3GPP, wireless devices or UEs always used the PRACH resource to send uplink data to a network when in the CELL_FACH state. Following the introduction of the common E-DCH in Release 8 of 3GPP, in order to send uplink data to a network when in the CELL_EACH state, the UEs that are not capable of using the common E-DCH always use the PRACH resource, whereas the UEs that are capable of using the common E-DCH always use the Release 8 common E-DCH resource (see for example the Release 8 Technical Specification 25.331).
Despite these known benefits of using the PRACH resource in certain circumstances, and indeed the requirement to use it in some circumstances (such as for older, legacy or other devices that cannot use common E-DCH), there is currently no process for balancing the uplink load between the PRACH and Release 8 common E-DCH resources that available for the wireless devices or UEs in a cell which are connected to a particular base station (or “Node B” as it is termed in the specific case of the Universal Mobile Telecommunications System (UMTS), eNodeB or Evolved Node B (eNB) in the case of LTE, etc.).